The invention presented herein relates to telephone trunk line testing circuitry for connection to a private branch exchange (PBX) and the telephone trunk lines for the PBX wherein the circuitry is operable from a remote location via a control trunk line to selectively isolate a trunk from the PBX and provide various connections to the selected trunk line and control trunk to carry out certain tests to determine whether the selected trunk is the source of a trunk transmission problem.
Trunk lines supplied by a telephone company for use by a private branch exchange (PBX) are to some extent repaired and maintained by the telephone company. A demarcation point exists near the PBX at which the trunk lines are connected with lines then connecting between the demarcation point and the PBX. The telephone company has responsibility only for the trunk lines between the demarcation point and the telephone company central office with the user of the PBX having responsibility for any lines and equipment on the PBX side of the demarcation point. This is a recent departure from past practice where the responsibility of the telephone company also extended to the PBX side of the demarcation point.
A problem is presented to the user of a PBX in that transmission problems can be encountered and it is not known on which side of the demarcation point the source of the problem exists. It is desirable that from the standpoint of time required to correct a problem as well as cost to the user of the PBX that the PBX user have a way for testing the trunk lines on the telephone company side of the demarcation to determine that the source of a problem that is within the telephone company's area of responsibility before requesting the service of the telephone company.
Prior efforts that have been made for making such tests include the use of test circuitry at the PBX end which can only be accessed from the central office or which require a direct dedicated circuit for reaching the test circuitry or the assignment of a line number to the test equipment. Other test equipment is known which is connected physically to one end of a trunk line which requires the connection of a special activation source from the other end of the circuit connected to the test equipment requiring use of such activation source at the telephone central office.